This invention relates to an improved method for preparing cyclicdicarboximido-substituted phosphonothioates corresponding to the general formula (I) ##EQU2## wherein in this and succeeding formula, R represents phthalimido ##SPC1##
Monomethyl substituted phthalimido ##SPC2##
4-cyclohexene-1,2-dicarboximido ##SPC3##
And monomethyl substituted 4-cyclohexene-1,2-dicarboximido ##SPC4##
In the present specification and claims, the term "loweralkoxy" refers to alkoxy radicals of from 1 to 4 carbon atoms, inclusive. Such radicals would be for example, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, secondary butoxy and tertiary butoxy. It is to be understood that the two loweralkoxy radicals may be the same or different.
In the present specification and claims, the term "loweralkyl" refers to alkyl radicals of from 1 to 4 carbon atoms, inclusive. Such radicals would be for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, secondary butyl and tertiary butyl.
Compounds of the above formula and methods for their preparation as well as a teaching of their utility as pesticides and as active toxicants in compositions for the control of insect, mite, helminth, plant, fungal and bacterial organisms are described in U.S. Pat. Nos. 3,336,188 and 3,450,713. The method taught by these references basically entails the reaction of an N-alkali metal derivative of a cyclicdicarboximido compound with an O,O-dialkylphosphorochloridothioate in the presence of an inert amido reaction medium such as, for example, N-methyl-2-pyrrolidone, dimethylformamide, hexamethylphosphoramide, N-acetylmorpholine and dimethylacetamide.
Another method of preparing the compounds of the present invention is taught in U.S. Pat. No. 3,399,213 wherein an alkali metal phosphoroamidothioate of the formula ##EQU3## IS REACTED WITH A CYCLICDICARBOXYLIC ANHYDRIDE OF THE FORMULA ##SPC5##
Wherein R' is hydrogen or a variety of other substituents, in the presence of an inert liquid reaction medium followed by the treatment of the product so produced with a ring-closing reactant such as phosphorus or sulfur based acid halides or an anhydride of an organic mono-, di-, or polycarboxylic acid.
While the above-described processes are effective to produce the compounds they are not entirely satisfactory because of their low yield and new and improved processes are continually being sought.